High resistance magnet and motor using the same

ABSTRACT

A magnet comprising grains of a ferromagnetic material whose main component is iron and a fluorine compound layer or an oxy-fluorine compound layer of fluoride compound particles of alkali metals, alkaline earth metals and rare earth elements, present on the surface of the ferromagnetic material grains, wherein an amount of iron atoms in the fluorine compound particles is 1 to 50 atomic %.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 11/838,266, filed Aug. 14, 2007 now U.S. Pat. No. 7,696,662, thecontents of which are incorporated herein by reference.

Claim of Priority

The present application claims priority from Japanese application serialNo. 2006-232989, filed on Aug. 30, 2006, the content of which is herebyincorporated by reference into this application.

DESCRIPTION OF THE INVENTION:

1. Field of the Invention

The present invention relates to a high resistance magnet, a method ofmanufacturing the magnet, a motor using the magnet and otherapplications of the magnet, and more particularly to a high resistance,high energy product magnet, a motor using the same and otherapplications thereof.

2. Related Art

In recent years, development of rare earth element magnets for magnetmotors has been conducted. The following patent document No. 1 disclosesrare earth element magnets with improved magnetic properties.

Patent document No. 1 discloses a rare earth element magnet with highcoercive force and high residual magnetic flux density well balanced byforming grain boundaries of a lamellar structure layer containingfluorine compounds at grain boundaries of rare earth element magnetrepresented by Nd-Fe-B. A thickness and coverage of the lamellarfluorine compound layer has been investigated.

Patent document No. 1: Japanese patent laid-open 2006-066859

SUMMARY OF THE INVENTION

In the patent document No. 1, improvement of magnetic properties of therare earth element magnet was realized by forming a lamellar fluorinecompound layer at the grain boundaries thereof. However, coercive force,residual magnetic flux density, rectangularity of demagnetization curve,thermal demagnetization properties, anisotropy, corrosion resistance,etc are not satisfactory. It is an object of the present invention toprovide a magnet having at least one of the improved properties abovementioned.

The present invention provides a magnet comprising grains of aferromagnetic material whose main component is iron and a fluoridecompound layer of fluoride compound particles of alkali metals, alkalineearth metals and rare earth elements, present on the surface of theferromagnetic grains, wherein an amount of iron atoms in the fluorinecompound particles is 1 to 50 atomic %.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing relationships among re-coil permeability andother electric properties.

FIGS. 2(1) to 2(8) are spectra of fluorine compounds measured by XRDanalysis.

FIGS. 3 to 5 are microscopic photographs of magnetic powders observed bya transmission electron microscope.

FIG. 6 is a cross sectional view of a motor according to an embodimentof the present invention.

FIG. 7 is a flow chart of forming a magnetic disc.

DESCRIPTION OF THE INVENTION

The iron maintains the crystal structure of the fluorine compound. Thegrains of the ferromagnetic material are ferromagnetic powder whosecomposition is represented by R-Fe-B wherein R is a rare earth element,Fe is iron and B is boron.

The particles of the fluorine compound are magnetic powder whose maincomponent is at least one of NdF₃, LiF, MgF₂, CaF₂, ScF₂, VF₂, VF₃,CrF₂, CrF₃, MnF₂, MnF₃, CoF₂, CoF₃, NiF₂, ZnF₂, AlF₃, GaF₃, SrF₂, YF₃,ZrF₃, NbF₅, AgF, InF₃, SnF₂, SnF₄, BaF₂, LaF₂, LaF₂, CeF₃, PrF₂, PrF₃,NdF₂, SmF₂, SmF₃, EuF₂, EuF₃, GdF₃, TbF₃, TbF₄, DyF₂, DyF₃, HoF₂, HoF₃,ErF₂, ErF₃, TmF₂, TmF₃, YbF₂, YbF₃, LuF₂, LuF₃, PbF₂, and BiF₃.

The particles of the oxy-fluorine compound, which is usable in thepresent invention as the ferromagnetic material is magnetic powder whosemain component is represented by Rw (O_(x)F_(y)) _(z) wherein w,x,y areintegers and R is at least one of Li, Mg, Ca, Sc, Mn, Co, Ni, Zn, Al,Ga, Sr, Y, Zr, Nb, Ag, In, Sn, Ba, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Pb and Bi.

The magnet according to claim 1, wherein an average particle size of thefluorine compound particles is 1 to 500 nm, and the fluorine compoundparticles have a higher electric resistance than the grains of theferromagnetic material.

The magnet has a recoil magnetic permeability of larger than 1.04, butsmaller than 1.30, and a specific resistance is 0.2 mΩcm or more. Thefluorine compound covers the surface of the ferromagnetic materialgrains in a coverage of 50 to 100%.

The grains of the fluorine compound particles grow when subjected tomolding under heating. The grains of the fluorine compound particleshave an average crystal grain size of 1 to 500 nm.

In the following, the present invention will be explained in detail byreference to drawings.

In the present invention, typical examples of the fluorine compounds arefluorides of metal elements represented by MF_(n) (M; metal element, F:fluorine, n: 1-4) and typical examples of oxy-fluorine compounds areoxy-fluorides of metal elements represented by M (0) F_(m) (m: 1-4).

The present invention is featured by forming a plate or lamellarstructure of a fluorine compound to thereby increase an interfacebetween a main phase and the fluorine compound and making the fluorinecompound to be a ferromagnetic phase.

As a method of forming the lamellar fluorine compound, there is asurface treatment. The surface treatment comprises a step of coating afluorine compound and/or an oxy-fluorine compound containing at leastone of alkali metals, alkaline earth metals and rare earth elements onthe surface of the ferromagnetic powder. In this method, a gelatinousfluorine compound or oxy-fluorine compound is crushed in an alcoholicsolvent and the solution is coated on the surface of the magneticpowder, followed by drying to remove the solvent.

The coating is heated at 200 to 400° C. to remove the solvent, and thenheated at 500 to 800° C. to thereby diffuse oxygen, rare earth elementsand elements constituting the fluorine compounds into the fluorinecompound and the ferromagnetic powder. The ferromagnetic powder contains10 to 5000 ppm of oxygen and light elements as impurities such as H, C,P, Si, Al, etc.

Oxygen contained in the ferromagnetic powder may be present as a phasecontaining oxygen in a mother phase or at grain boundaries in acomposition displaced from stoichiometric relation as well as in theform of oxides of rare earth elements, Si, Al, etc. The oxygencontaining phase make worse magnetization of the ferromagnetic powder,and gives influence on the magnetization curve. That is, this leads todecrease in residual magnetic flux density, anisotropic magnetic field,rectangularity of magnetization curve and coercive force and increase inirreversible demagnetization ratio and thermal demagnetization, andfluctuation of magnetization property, deterioration of corrosionresistance, lowering of mechanical properties, etc.

Since oxygen gives influences on various magnetic properties, it hasbeen attempted to prevent oxygen from remaining in the ferromagneticpowder.

When the ferromagnetic powder having the fluorine compound layer isheated to 400° C. or higher, diffusion of iron into the fluorinecompound takes place. Iron atoms in the ferromagnetic powder arecontained as an intermetallic compound with rare earth elements. Wheniron atoms are heated, iron atoms diffuse into the fluorine compoundlayer. In forming the fluorine compound layer on the surface of theferromagnetic powder, rare earth fluoride REF₂ or REF₃ where RE is arare earth element is heated at 400° C. or lower to grow its crystal;then, the crystal is maintained in a vacuum of 1×10⁻⁴ torr or less at500 to 800° C. for 30 minutes. This heat treatment effects diffusion ofiron atoms into the fluorine compounds and at the same time the rareearth elements in the ferromagnetic material powder into REF₃, ReF₂ orRE (OF), or grain boundaries of the compounds.

The fluorine compounds or oxy-fluorine compounds have a crystalstructure of a face-centered cubic lattice; a lattice constant is from0.54 to 0.60 nm. By controlling an amount of iron in the fluorinecompounds and oxy-fluorine compounds, the residual magnetic fluxdensity, anisotropy, corrosion resistance, etc can be remarkablyimproved.

In order to obtain a density of 90% or more at the time of molding underheating, the temperature for molding should be as high as 500 to 800° C.thereby to soften the mother phase. The molding at the temperature growsthe crystal grains of fluorine compounds or oxy-fluorine compounds anddiffusion between the ferromagnetic material powder and the fluorinecompounds or oxy-fluorine compounds.

If the temperature exceeds 800° C., a soft magnetic material such asαFe, etc grows. Therefore, the molding under pressure is carried out ata preferable molding temperature lower than 800° C. If the formation ofthe soft magnetic material is controlled by adding various additiveelements, a molding temperature higher than 800° C. may be acceptable.In case where the ferromagnetic material powder is NdFeB group, Nd, Fe,B or additive elements diffuse into fluorine compounds that grow byassistance of a grain boundary stress generated by the heating at 500°C. or higher under pressure. At the above temperature, a portion where aconcentration of Fe is 1 atomic % (grain boundaries or defects) appears,though the concentration differs depending on locations. If thetemperature is lower than 500° C., a high pressure is needed to deformhard NdFe powder, which needs a high price metal mold and shortens thelife of the mold.

A driving force of diffusion is a temperature, stress (strain),concentration difference, defects, etc, the diffusion being observed bymeans of a microscope, for example. Although elements such as Nd, B, etcdo not change greatly magnetic properties of the fluorine compounds, itis possible to keep constant the magnetic properties of the magnet bycontrolling a concentration of Fe because Fe atoms change the magneticproperties of the fluorine compounds based on its concentration. When atotal concentration of elements other than B is 100%, and when aconcentration of Fe is set to 50 atomic % or less, a structure of thefluorine compound can be maintained. If the Fe concentration exceeds 50atomic %, an amorphous phase or an Fe main phase appears thereby tobecome a mixed phase with a small coercive force. Accordingly, the Feconcentration should be 50 atomic % or less.

The NdFeB magnetic material powder contains magnetic powder containing aphase equivalent to a crystal structure of Nd₂Fe₁₄B in a mother phase.The mother phase may contain transition metals such as Al, Co, Cu, Ti,etc. A part of B may be replaced with C. Compounds such as Fe₃B orNd₂Fe₂₃B₃, etc or oxides may be contained in a layer other than themother layer.

When the fluorine compound phase is formed in the Sm₂Co₁₇ magneticpowder, followed by heating and molding it, Co diffuses into thefluorine compound layer. When an amount of Co diffusion is large, Co inthe fluorine compound becomes soft magnetic thereby to increase a loss.In order to reduce the loss, a Co concentration in the fluorine compoundlayer is lowered to 50 atomic % or less.

Since the fluorine compound layer exhibits resistance higher than thatof NdFeB magnetic powder at 800° C. or lower, it is possible to increaseresistance of the NdFeB sintered magnet by forming the fluorine compoundlayer so that the loss can be reduced. The fluorine compound layer maycontain such impurities besides the fluorine compound that do notexhibit ferromagnetism at around room temperature, which has littleinfluence on magnetic properties. In order to obtain a high resistance,the fluorine compound layer may contain fine particles of nitrogencompounds or carbides.

As has been discussed, when a layer containing fluorine compound on theiron group magnetic material powder is formed, followed by heattreatment and molding, a molding with balanced low coercive force andhigh magnetic flux density can be provided. When such molding is appliedto an electric rotating machine, a low loss and high induction voltageare realized. The molding is also applied to magnetic circuits includingvarious electric rotating machines.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, preferred embodiments for practicing the presentinvention are explained.

Embodiment 1

Quenched powder containing a main amount of Nd₂Fe₁₄B was prepared asNdFeB group powder. The quenched powder contained Nd₂Fe₁₄B as a mainphase, Nd rich phase and B rich phase such as Nd_(1.1)Fe₄B₄. In theexamples of the specification, the NdFeB powder is the same material asmentioned above, otherwise specified. A fluorine compound was formed onthe surface of the powder. When NdF₃ is formed on the quenched powder,Nd(CH₃COO)₃ as a starting material was dissolved in water and HF wasadded thereto. When HF was added, gelatin of NdF₃ xH₂O was formed. Theresulting product was centrifuged to remove the solvent. The product wasadmixed with NdFeB powder and was coated. The solvent of the mixedproduct was vaporized and heated to evaporate hydrolyzed water. Theresulting film was subjected to analysis with XRD (energy diffraction Xray analysis).

The film was formed along the uneven surface of the NdFeB powder. As aresult, it was revealed that the film comprised NdF₃, NdF₂, NdOF, etc.When the powder having a particle size of 1 to 300 μm was heated, whilepreventing oxidation, at a temperature lower than 800° C. at whichmagnetic properties become worse, magnetic powder with a high resistancelayer and a residual magnetic flux density of 0.7T or more was produced.

If the powder has a particle size of less than 1 μm, the powder iseasily oxidized, and if the particle size is larger than 300 μm,improvement of magnetic properties by forming the high resistance filmand the fluorine compound is insufficient. The magnetic powder wascharged in a metal mold to pre-mold it under a compression pressure of2t/cm², and it was pressure-molded in a larger mold at a temperature of500 to 800° C., without taking out the molding from the mold into anatmosphere. At this stage, the fluorine compound and magnetic powderwhose main component is Nd₂Fe₁₄B as the mother phase in the mold aredeformed under a load of 3t/cm² thereby to exhibit magnetic anisotropy.As a result, a high resistance magnet having a residual magnetic fluxdensity of 1.0 to 1.4 T and a specific resistance of 0.2 to 2 mΩcm wasobtained.

A rectangularity of demagnetization curve of the molding depends onmolding conditions and fluorine compound forming conditions. This isbecause a direction of c-axis of the mother phase crystal of Nd₂Fe₁₄B isdifferent depending on molding conditions and fluorine compound formingconditions.

Further, it was revealed by analysis of structure and composition of themolding with a transmission electron microscope that an inclined angleof demagnetization curve of the molding in the vicinity of the zeromagnetic field depends on the distribution degree of the c-axis andstructure and composition in the vicinity of interfaces between thefluorine compound and the magnetic material powder. When a density ofthe molding is 90 to 99%, the fluorine compound layer integrates,diffuses and grows in the molding; the molding is partially sinteredwherein the fluorine compound is a binder.

In case where the thickness of the fluorine compound layer is about 500nm, a particle size of the fluorine compound immediately after moldingis 20 nm and the particle size in the molded powder was 30 nm; thefluorine compound layers formed on the surfaces of different magneticmaterial powder are bonded wherein there were many points where crystalgrains grow and are sintered. It was revealed that Fe was present in thegrown crystals of fluorine compound. Because Fe was not present in thefluorine compound before crystal grain growth, it is though that Femoved by diffusion from the magnetic material powder at the time ofcrystal grain growth.

It is presumed that rare earth elements and oxygen that are present inthe surface of the magnetic material powder also diffuse simultaneouslywith Fe. The fluorine compound into which Fe diffuses contains more NdF₂than NdF₃. A concentration of Fe in the fluorine compound measured byXRD analysis was 1 to 50% on average. The fluorine compound wasamorphous around the composition of 50% of Fe. Because oxygen wascontained, it was revealed that besides NdFeB magnetic powder whose maincomponent is Nd₂Fe₁₄B mother phase, there were NdFeF₂, NdF₃, Nd (O,F)and amorphous NdFeFO, and 1 to 50 at % of Fe on average was contained inthe fluorine compound and oxy-fluorine compound. Although it is notprecisely revealed that Fe atoms are present at which sites, it ispresumed that Fe atoms are replaced with fluorine atoms or rare earthelements.

The balanced high residual magnetic flux density and high resistance areachieved the fluorine compound is formed in R-Fe-X (where R is a rareearth element, X is a third element) or an R-T compound (where R is arare earth element and T is Fe, Co or Ni). The crystal grains in thefluorine compound grow to diffuse into the mother phase; sintering ofthe crystal grains takes place by means of the fluorine compound as asintering binder. As these fluorine compounds, RFn (n is 1 to 3), whichconsisting essentially of R selected from the group consisting of one of3d transition elements selected from Li, Mg, Ca and rare earth elementsand fluorine, which is produced by sintering under pressure and contains1 to 50 atomic %. If a concentration of Fe in the fluorine compound islarger than 50 atomic % until 80 atomic %, apart of fluorine compoundbecomes amorphous, which may make magnetic properties worse.Accordingly, molding conditions and forming conditions of fluorinecompounds should be properly selected to achieve a concentration of Feto be 50 atomic % or less, thereby to avoid deterioration of magneticproperties.

Besides NdF₃ there are as fluorine compounds NdF₃, LiF, MgF₂, CaF₂,ScF₂, VF₂, VF₃, CrF₂, CrF₃, MnF₂, MnF₃, CoF₂, CoF₃, NiF₂, ZnF₂, AlF₃,GaF₃, SrF₂, YF₃, ZrF₃, NbF₅, AgF, InF₃, SnF₂, SnF₄, BaF₂, LaF₂, LaF₂,CeF₃, PrF₂, PrF₃, NdF₂, SmF₂, SmF₃, EuF₂, EuF₃, GdF₃, TbF₃, TbF₄, DyF₂,DyF₃, HoF₂, HoF₃, ErF₂, ErF₃, TmF₂, TmF₃, YbF₂, YbF₃, LuF₂, LuF₃, PbF₂,and BiF₃. When these fluorine compounds are surface-treated with asolution containing a compound having oxygen or carbon, oxy-fluorinecompounds are obtained. When a concentration of Fe of 1 to 50 atomic %in the compounds, a recoil magnetic permeability can be controlled to be1.05 to less than 1.30 thereby to reduce a loss of the magnet.

Embodiment 2

A DyF₃ layer or TbF₃ layer was formed on Nd₂Fe₁₄B magnetic powder with ahigh residual magnetic flux density to which an additive element with ahigh coercive force such as Dy, Tb or Pr is not added, thereby toachieve a high residual magnetic flux density and high coercive force.An alloy having a composition close to Nd₂Fe₁₄B was melted by a highfrequency melting to produce a cast ingot. The ingot was crushed by acrusher to obtain powder having a particle size of 1 to 10 μm.

In order to form a fluorine compound layer on the powder, a treatingsolution, which was prepared by gelatin DyF₃.XH₂O or TbF₃.XH₂O wascentrifuged to remove a solvent, was admixed with the above powder. Thesolvent of the mixture was evaporated and the mixture was heated toremove hydrated water.

The resulting powder was press-molded in a lateral magnetic field or avertical magnetic field of 11 thereby to orient the magnetic powder.Thereafter, the powder was sintered in vacuum at a temperature of 900 to1100° C. for 4 hours; followed by heat-treating it at 600° C. to obtaina sintered body with a density of 90 to 99% with respect to thetheoretical density. When the Dy fluorine compound is formed, thefluorine compound in the sintered body is composed of DyF₂, DyF₃,Dy(O,F), etc; diffusion of Fe or Nd into the fluorine compounds whensintered.

If a content of Fe in the fluorine compound becomes large, it isdifficult to achieve the high coercive force. Thus, it is necessary tolimit the content to 50 atomic %.

The Dy and Tb segregate in the vicinity of grains after sintering tothereby achieve the high residual magnetic flux density and highcoercive force. As described above, when the fluorine compound havingthe rare earth element rich phase, which contributes to the highresidual magnetic flux density and high coercive force, is formed on thesurface of the magnetic powder by surface treatment to produce asintered magnet with a residual magnetic flux density of 1.3 to 1.6 Tand a coercive force of 20 to 35 kOe and with a good rectangularity.

Before charging the quenched magnetic powder, which is surface treatedwith the fluorine compound, in the press mold, the powder is heattreated at a temperature of 500 to 800° C. The heat treatment formsportions containing 1 atomic % of Fe and effect diffusion of rare earthelements. A heat treatment at a temperature higher than 800° C. effectsgrowth of a soft magnetic phase such as αfe and deteriorates magneticproperties. Improvement of magnetic properties by the heat treatment at500 to 800° C. includes increase in coercive force and rectangularity,improvement of temperature property, and high resistance. The magnet canbe produced by molding together with an organic binder.

Embodiment 3

Quenched powder whose main component is Nd₂ (Fe, Co)₁₄B as NdFeB grouppowder was prepared. A fluorine compound was formed on the surface ofthe quenched powder. The quenched powder may contain amorphous portions.In forming DyF₃ on the surface of the quenched powder, a solution of Dy(CH₃COO)₃ was dissolved in water and HF was added to produce gelatinDyF₃.xH₂O. The resulting compound was subjected to centrifugation toremove a solvent. The resulting was admixed with NdFeB powder. Thesolvent of the mixture was vaporized and the mixture was heated toremove hydrated water.

The resulting fluorine compound layer having a thickness of 700 μm wasinvestigated by an XRD. As a result, it was found that the fluorinecompound film comprised DyF₃, DtF₂, DyOF, etc. The magnetic powderhaving a particle size of 1 to 300 μm was heated at a temperature lowerthan 800do° C. at which the magnetic properties become worse, whilepreventing oxidation, to produce magnetic powder having a highresistance layer and a residual magnetic flux density of 0.7T or more.It was confirmed that the coercive force and rectangularity of themagnetic powder were improved by heating at 350 to 750° C.

In the particle size is less than 1 μm, the powder is easily oxidized tomake the magnetic properties worse, and if the particle size is largerthan 300 μm, effects of high resistance and of magnetic propertyimprovement, which is caused by forming the fluorine compound, areunsatisfactory.

The magnetic powder was charged in a mold and pre-molded under acompression pressure of 1t/cm², followed by pressure-molding thepre-molding in a larger mold at a temperature of 400 to 800° C., withouttaking out the pre-molding into the atmosphere. The fluorine compoundand the magnetic powder whose main component is Nd₂Fe₁₄B in the moldwere deformed under a pressure of 1t/cm² or more to realize magneticanisotropy. As a result, the residual magnetic flux density became 1.0to 1.4T and a high specific resistance became 0.2 to 20 mΩcm.

A rectangularity of demagnetization curve of the molding depends onmolding conditions and the molding conditions of the fluorine compound.This is because orientation of c-axis, which is a crystal axis of themother phase, i.e. Nd₂Fe₁₄B, differs in accordance with the moldingconditions and molding conditions of fluorine compound.

Further, it was revealed by structure analysis and composition analysiswith a transmission electron microscope that an inclination of thedemagnetization curve of the molding in the vicinity of zero magneticfield depends on distribution degree of the c-axis and a structure andcomposition in the vicinity of the interface between the fluorinecompound and magnetic powder. In a molding having a density of 90 to99%, the fluorine compound brings about integration, diffusion and graingrowth, and is partially sintered wherein the fluorine compound layer onthe magnet powder is a binder.

When a thickness of the fluorine compound layer is 500 nm, a particlesize of the fluorine compound immediately after the formation of thefluorine compound on the magnetic powder is 1 to 100 nm, but a particlesize of the fluorine compound in the molding is 10 to 500 nm, whereinthe fluorine compound layers on different magnetic powder bond andintegrate to grow inside the bonded fluorine compound layers. It wasrevealed that iron, cobalt and Nd were present in the fluorine compound.Since iron was not present in the fluorine compound before the graingrowth, it is thought that iron diffused and transferred from themagnetic powder at the time of grain growth. It is presumed that withdiffusion of iron, rare earth elements and oxygen that was present inthe surface of the magnetic powder diffused.

Fluorine compound into which iron diffuses contains more DyF₂ than DyF₂.A surface concentration of iron in the fluorine compound, which wasmeasured by EDX analysis, was 1 to 50 at % on average. If theconcentration of iron is about 50% or more, the fluorine compound wasamorphous. Because oxygen was contained, it is presumed that besidesNdFeB magnetic powder whose main component is Nd₂Fe₁₄B, (Dy, Nd) F₂,NdF₃, Nd (O, F) and amorphous DyFeFO were present in the molding andthat 1 to 50% of iron on average was contained in the fluorine compound.

Although it has not been confirmed precisely that iron atoms arearranged in which sites, it is presumed that they are arranged atfluorine atoms or rare earth elements to replace them. The balanced highresidual magnetic flux density and high resistance are realized byforming Nd-Fe-X (X is a third element such as B or C) or Nd-Fe compoundsuch as Nd₂Fe₁₇, Nd₂Fe₁₉) , and by effecting diffusion reaction with amother phase when crystal grains grow in the fluorine compound layer,wherein the fluorine compound layer works as a binder for sintering.

The fluorine compound layer can be used as a binder for NdFeB groupmagnets, SmCo group magnets, amorphous alloys, which is a Fe group softmagnetic material, silicon steel plate, and electromagnetic stainlesssteel. When the materials are irradiated with a millimeter-wave ormicrowave, the fluorine compound is selectively bonded by heatgeneration.

Embodiment 4

Quenched powder whose main component was Nd₂ (Fe, Co)₁₄B was prepared asNdFeB group powder, and fluorine compound was formed on the surface ofthe powder. The quenched powder was flake powder having a thickness of15 to 50 μm. The powder may contain amorphous phase.

In forming NdF3on the surface of the quenched powder, Nd(CH₃COO)₃ as astaring material was dissolved in water and HF was added to thesolution. By adding HF to the solution, gelatin form NdF₃.xH₂O wasformed. The gelatin was subjected to centrifugation to remove thesolvent. The resulting was admixed with NdFeB powder. The solvent of themixture was evaporated to remove it and it was heated to remove hydratedwater.

A resulting fluorine compound layer of 100 nm thick was subjected to XRDanalysis. As a result, it was revealed that the fluorine compound layerwas composed of NdF₃, NdF₂, NdOF, etc. When the magnetic powder having aparticle size of 1 to 300 μm was heat-treated, while preventingoxidation, at a temperature of 700° C. at which magnetic properties aredeteriorated, magnetic powder having a high resistance layer and aresidual magnetic flux density of 0.7T or more was obtained. At thistime, it was confirmed that coercive force and rectangularity of themagnetic powder were improved when the magnetic powder was heat-treatedat 750° C. If the particle size is less than 1 μm, the magnetic powderis easily oxidized so that magnetic properties become worse. Further, ifthe particle size is larger than 300 μm, improvement of magneticproperties by high resistance and formation of fluorine compound will beinsufficient.

In molding, the magnetic powder is charged in a mold to mold it under apressure at a temperature of 800° C. As a result, a molding having aresidual magnetic flux density of 0.7 to 0.9T and a specific resistanceof 0.2 to 20 mΩcm was obtained. The molding has different densitiesdepending on heating-molding conditions; in order to obtain a density of90% or more, press-molding at 500 to 800° C. is preferable. Although ahigh density is expected by molding at a high temperature, otherelements tend to diffuse into the fluorine compound layer. Therefore,molding at a low temperature is preferable.

FIG. 4 shows a transmission electron microscope photograph of asectional view of a sample, which was obtained by molding magneticpowder having a NdF₃ layer of 100 nm thick thereon. In FIG. 4, an areacircled by a dotted line is NdF₃ layer and an area A circled by a solidline is particles of NdF₃. After coating of NdF₃, the NdF₃ particles inthe NdF₃ layer had a particle size of 1 to 20 nm. By press-molding, theNdF₃ particles grow to become particles having 100 nm or more. FIGS. 2(1), 2 (2) show EDX analysis profiles of NdF₃ particles in the area A.FIG. 2 (1) shows the result obtained from point 1 in the area A, andFIG. 2 (2) the result obtained from point 2 in the area A. There areobserved in the profile signals of Nd, Fe, F, O, Mo and Ga. Mo is asignal from a mesh on which the sample was placed, not from the molding.Ga is a signal from ions irradiated for making a thin film.

Fe was not observed in the profile of NdF₃ or NdF₂ layer immediatelyafter the formation of coating; it is presumed that Fe diffused into thefluorine compound at the time of heat-molding. Fe was observed in areasother than the area A; a concentration of Fe was 1 at % or more (anamount of Fe per the total amount except B).

FIG. 5 shows a transmission electron microscope photograph of a crosssection of a sample, which was obtained by molded at a temperaturehigher than that used for molding of the sample shown in FIG. 4. In FIG.5, crystal grains (about 200 nm in size) of an Nd fluorine compoundlarger than those in FIG. 4 were observed. EDX profiles measured forgrains in area B and area C are shown in FIGS. 2 (3), 2 (4) and 2 (5).FIGS. 2 (3) and 2 (4) correspond to point 3 in the area B and FIG. 2 (5)corresponds to point 5in the area C.

Fe was observed in any of the profiles (3) to (5) of at least 1 atomic%. Since the crystal grains were NdF₂, it is presumed that Fe replacedin lattices of the NdF₂ crystal.

FIG. 6shows a transmission electron microscope photograph of a crosssection of a sample, which was molded at a temperature further higherthan that of the sample shown in FIG. 5. In case of FIG. 6, grainboundaries became unclear and a sample having an average size of 500 nmwas found. EDX analysis profiles measured on grain areas 6, 7 and 8 ofNdF₃ in FIG. 6 are shown in FIGS. 3 (6), 3(7), 3(8). The relationshipbetween FIG. 6 and FIGS. 3(6), 3(7) and 3(8) are the same as thatbetween FIG. 5 and FIGS. 2(3), 2(4) and 2(5). It is seen in FIGS.3(6)-3(8) that a peak of Fe representing a concentration of Fe atoms ishigher than that of Nd in a range of from 4.0 to 8.0 keV.

On the other hand, it is seen from a diffraction pattern that a portionof F is NdF₂, which has a concentration of Fe smaller than that inamorphous phase. The Fe concentrations in D and F are larger than 50%,but in F the concentration is less than 50%. According to these facts,it is revealed that growth of a layer having a Fe concentration of 50%or more and an amorphous phase is suppressed by controlling the Feconcentration in the fluorine compound layer or oxy-fluorine compoundlayer. For this purpose, low temperature press-molding or short timemolding in a low oxygen concentration are exemplifies as heat-pressmolding conditions. By controlling the Fe concentration in the fluorinecompound layer to 50% or less, it is possible to realize ademagnetization curve has a recoil magnetic permeability of 1.04 to1.30.

Embodiment 5

Hydrogen treated powder whose main component was Nd₂Fe₁₄B was preparedas NdFeB powder, and fluorine compound was formed on the surface of thepowder.

In case of NdF₃ coating, a semi-transparent sol state solution having anNdF₃ concentration of 1 g/10 mL was used in the following steps.

-   (1) 15 mL of NdF₃ coating film forming treating solution was added    to 100 g of rare earth element magnetic powder having an average    particle size of 70 to 150 μm, and the mixture was stirred until the    whole of magnetic powder was wet.-   (2) Methanol was removed in a reduced pressure of 5 torr from the    above (1) magnetic powder treated with the NdF₃ coating film    treating solution.-   (3) The magnetic powder from which the solvent was removed was    charged in a mortal boat, and heat-treated at 200° C. for 30 minutes    and 400° C. for 30 minutes under a pressure of 1×10⁻⁵ torr.-   (4) Magnetic properties of the rare earth magnetic powder subjected    to heat treatment at (3) were investigated.

The film was investigated with XRD. As a result, it was confirmed thatthe fluorine compound layer was composed of NdF₃, NdF₂, NdOF, etc. Whenthe powder having a particle size of 50 to 150 μm was heated at 800° C.,while preventing oxidation of the powder, a high resistance layer wasformed on the surface thereof. If a particle size is less than 1 μm, thepowder is easily oxidized so that magnetic properties become worse. Ifthe particle size is larger than 300 μm, an improvement of magneticproperties by making high resistance and forming of fluorine compoundwill be insufficient.

After the magnetic powder is charged in a mold and was press pre-moldedunder a load of 2t/cm² in a magnetic field, it was further sintered inthe mold at 800° C., without taking out the molding into the atmospherefrom the mold. As a result, the residual magnetic flux density of themolding was 1.0T to 1.4T and a specific resistance was 0.2 to 2 mΩcm toproduce a high resistance magnet.

Rectangularity of demagnetization of the mold depends on orientationconditions, sintering conditions of the magnetic powder and formingconditions of the fluorine compound.

An inclination of the demagnetization of the molding in the vicinity ofa zero magnetic field depends on distribution of the c-axis orientationand a structure and composition in the vicinity of interfaces betweenthe fluorine compound and magnetic powder.

If the molding has a density of 90 to 99%, the fluorine compound layerintegrate, diffuse and grow during molding so that the fluorine compoundlayer on the magnetic powder is a binder for sintering to effect apartial sintering. If the fluorine compound layer has a thickness ofabout 500 μm, the particle size of the fluorine compound immediatelyafter the forming the fluorine compound on the magnetic powder is 1 to30 μm. The particle size of fluorine compound during molding becomes 10to 500 μm, wherein the fluorine compound layers formed on differentsurfaces of the magnetic powder bond each other and crystal grains growin the bonded fluorine compound layers; many sintered portions wereobserved.

It was also confirmed that there was Fe in the crystals of fluorinecompound. Because Fe was not present in the fluorine compound beforegrain growth of the fluorine compound, it is presumed that Fe diffusedand moved from the magnetic powder at the time of grain growth. It isalso presumed that rare earth elements and oxygen that was present onthe surface of the magnetic powder diffuse together with iron. Fediffuses more into NdF₂ than in NdF₃.

A concentration of Fe in the fluorine compound that measured by EDXanalysis was 1 to 50% on average. The fluorine compound was amorphousaround 50% of Fe concentration.

It was revealed that since oxygen was present, NdF₂, NdF₃, Nd(O,F), andNdFeO amorphous phase, Nd rich phase and B rich phase were present inaddition to NdFeB magnetic powder whose main component is Nd₂Fe₁₄Bmother phase and that Fe of 1 to 50% was contained in the fluorinecompound and/or oxy-fluorine compound. Although it is not elucidatedprecisely yet where iron atoms are present, it is presumed that ironatoms replace fluorine atoms or rare earth element.

The balanced high residual magnetic flux density and high resistance arerealized when fluorine compound is formed on Nd-Fe-X (X: B or C as athird element) or Nb-Fe such as Nd₂Fe₁₇ or Nd₂Fe₁₉, and when crystalgrains in the fluorine compound grow to effect diffusion reaction withthe mother phase and the fluorine compound becomes a binder forsintering. Such fluorine compounds as RF_(n) (n is an integer of 1 to 3)or R_(w) (O_(x)F_(y))_(z) wherein w, x and y are integers and R is amember selected from the group consisting of Li, Mg, Ca, Sc, Mn, Co, Ni,Zn, Al, Ga, Sr, Y, Zr, Nb, Ag, In, Sn, Ba, La, Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, Lu, Pb and Bi. The fluorine compounds comprises anelement selected from Li, Mg, Ca, 3d transition elements or rare earthelements and fluorine containing Fe of from 1 to 50%. If theconcentration of Fe in the fluorine compound exceeds 50%, i.e. more than50 to 80%, a part of fluorine compound becomes amorphous to deterioratemagnetic properties. Thus, it is necessary to choose conditions ofheating, pressure and forming of fluorine compound so as to control theFe concentration to be 50% or less.

A molded sample of NdFeB group ferromagnetic material having a Nd₂Fe₁₄Bcrystal structure and having a density of 95 to 98% was coated with anNdF₃ or NdF₂ layer. The sample was subjected to evaluation of loss at afrequency of 1 kHz thereby to calculate an eddy current loss andhysteresis loss.

FIG. 1 shows a relationship between a recoil magnetic permeability andspecific resistance and a relationship between the recoil magneticpermeability and various losses. The abscissa indicates the recoilmagnetic permeability, and the ordinate indicates the specificresistance, eddy current, hysteresis loss and a total loss of the eddycurrent plus the hysteresis loss.

As is understood from FIG. 1, the specific resistance increases as therecoil magnetic permeability increases. However, the total loss of theeddy current loss plus the hysteresis loss does not decrease even if thespecific resistance and the recoil magnetic permeability are large. Itis said from the result of tests that the recoil magnetic permeability,which can reduce the loss most, is within a range of from 1.04 to 1.3.If the permeability exceeds 1.3, the magnetic powder has a loss largerthan that of NdFeB molding.

When a thickness of the fluorine compound layer is made thicker and themolding is heated at a temperature higher than 800° C. in order toincrease the specific resistance, Fe diffuses to increase a softmagnetic component and the recoil magnetic permeability as well. Thisleads to an increase in the hysteresis loss, and further to an increaseof the total loss.

In order to avoid an increase in the recoil magnetic permeability, it isnecessary to control an amount of diffused Fe in the fluorine compoundto be less than 50%. Accordingly, it is preferable to conduct themolding at a temperature range of from 500 to 800° C., particularly atrelatively low temperature of the above temperature range to therebycontrol a thickness of fluorine compound layer to be 300 nm or less andto prevent diffusion of Fe into the fluorine compound layer.

Embodiment 6

After oxides are removed by acid-washing the surface of the Nd₂Fe₁₄Bsintered magnet, NdF₃ was formed on the surface of the sintered magnetin the following manner.

As a starting material, Nd(CH₃COO) ₃ was dissolved in water, and HF wasadded to the solution. By adding HF, gelatin like NdF₃.xH₂O was formed.The gelatin was subjected to centrifugation to remove water. Theresulting gelatin was coated on the surface of the Nd₂Fe₁₄B sinteredbody. The solvent of the coating was evaporated and the coating washeated to evaporate hydrated water. The coating was subjected to XRDanalysis. As a result, it was revealed that the fluorine compound layerwas composed of fluorine compounds and oxy-fluorine compounds such asNfdF₃, NdF₂, NdOF, etc.

The resulting sintered body was heated at 600° C., preventing oxidation,thereby forming a high resistance layer on the surface.

When the magnets having a high resistance layer are stacked, it ispossible to lower an eddy current loss when the magnets are exposed to ahigh frequency magnetic field.

Since the fluorine compound generates heat when it is irradiated withmillimeter-wave, magnets with a fluorine compound layer can be bonded byirradiating them with the millimeter-wave (frequency; 29 GHz) so thatthe fluorine compound layer selectively generates heat and bond themagnets. Heat generation of an interior of the magnets is suppressed,and reaction between rare earth elements in the fluorine compound orcomponents for a mother phase and fluorine compound proceeds.

Upon irradiation with millimeter-wave, iron atoms diffuse into thefluorine compounds to be 1% on average. High resistance layers wereformed on the surfaces of sliced magnets having a thickness of 0.1 to 10mm thick. When the magnets are irradiated with millimeter-wave, thefluorine compound is selectively heated to thereby form a low losssintered magnet.

Fluorine compound includes RFn (n: 1 to 3, R: rare earth element) thatcontains at least one of alkali metals, alkaline earth metals, and rareearth elements. By millimeter-wave irradiation or microwave irradiation,the oxy-fluorine fluorine compound containing Fe grows. The abovemanners can be applied to sintered magnets of different sizes.

Example 7

Quenched magnetic powder whose main component is Nd₂Fe₁₄B was preparedas NdFeB powder. Fluorine compound was formed on the surface of thepowder. The fluorine compound was formed on the surface of Fe group softmagnetic powder, too.

The NdFeB group magnetic powder and Fe group magnetic powder wereseparately pre-molded, and at least two pre-moldings were simultaneouslypress-molded to produce a molding including a soft magnetic material andhard magnetic material so that a magnetic circuit with a low loss wasrealized.

In forming NdF₃ as a high resistance film on the quenched powder,Nd(CH₃COO)₃ was dissolved in water and HF was added to the solution. Byadding HF, gelatin like NdF₃.xH₂O was formed. The gelatin was subjectedto centrifugation to remove the solvent. The resulting gelatin wasadmixed with the NdFeB powder. The solvent of the mixture was evaporatedand hydrated water was vaporized by heating. The gelatin was admixedwith the Fe −3% Si magnetic powder. The solvent of the mixture wasevaporated and hydrated water was vaporized by heating.

It was confirmed by XRD that the fluorine compound was composed of NdF₃,NdF₂, NdOF, etc. The resulting phases of the NdFeB magnetic powder andFe −3% Si magnetic powder had a high resistance until 800° C.

NdFeB group magnetic powder with the fluorine compound layer wasdeformed at 650° C. to exhibit anisotropy and improved magneticproperties. Fe group soft magnetic powder with the fluorine compoundlayer was molded at the above temperature. Hysteresis loss was reducedby heating for stress-releasing after molding, and an eddy current losswas reduced because the high resistance was maintained.

Since molding at 650° C. is a temperature at which the NdFeB magneticpowder with the fluorine compound layer and the Fe magnetic powder withthe fluorine compound layer are press-molded, keeping the highresistance and magnetic properties, a density of 90 to 99% could bemaintained. In this case, there is fluorine compound between NdFeBmagnetic powder and Fe magnetic powder; deformation, diffusion andbonding of the fluorine compound form the molding.

The use of fluorine compound reduces a difference in thermal expansioncoefficients. Since the above method is different from the anisotropyimparting molding method, the materials can be molded simultaneously.Depending on the shapes of parts, after molding the NdFeB magneticpowder, the Fe magnetic powder is molded at around room temperature, anda stress releasing heat treatment is applied at last.

Embodiment 8

After a Ta under layer having a thickness of 10 nm or more was formed ona glass substrate by a sputtering method, a NdFeB thick film having athickness of 10 to 100 μm was formed on the Ta under layer.

In forming DyF₃, Dy (CH₃COO) ₃ was dissolved in water, and HF was addedthereto to form gelatin like DyF₃.xH₂O. The gelatin was centrifuged andwas coated on the thick film. Thereafter, the solvent was removed, andhydrated water was evaporated by heating. DyF₃ or DyF₂ was grown on thesurface of the NdFeB thick film. A thickness of fluorine compounds were1 to 100 nm and 30 nm on average.

A millimeter-wave or microwave was irradiated on the fluorine compoundfilm to heat the film to diffuse Dy or F atoms into the surface of theNdFeB film. As a substrate, SiO₂ group glass, which is hard to be heatedby millimeter-wave or microwave is preferable.

Fe and Nd diffuse together with Dy and F so that 1 at % of Fe wasobserved in the fluorine compound, and rectangularity and coercive forceof the NdFeB were improved. The thick film magnet had a residualmagnetic flux density of 0.7 to 1.1 and a coercive force of 10 to 20kOe.

Embodiment 9

In FIG. 7 showing a cross sectional view of a motor, a permanent magnet11 was brought into contact with a soft magnetic material 12. Thepermanent magnet and the soft magnetic member 12 constitute a rotor 16.The rotor 16 is supported by a shaft 13 by means of a fixing member 17.The permanent magnet 11 had a thickness of 500 μm. In order to improvemagnetic properties of the permanent magnet 11, a fluorine compound wascoated on the permanent magnet 11 to grow fluorine compound particles of10 nm on the permanent magnet. Then, the coating was heated at 400 to800° C. to improve coercive force. The stator 15 to which a stator coil14 is fixed.

The fluorine compound is an oxygen containing fluorine compound such asDy(OF), Nd(OF), a carbon containing fluorine compound such as Dy(O,F,C),which are formed in lamellar form by surface treatment with DyFe or analcohol solution containing DyF₂. The fluorine compound is a permanentmagnet constituting Nd₂Fe₁₄B whose main structure is a cubic crystal.

The permanent magnet may be either a thick film or sintered magnet. Ashaft 13 was inserted and a coil 14 was disposed. The heating can beconducted by millimeter-wave.

According to the present invention, it is possible to provide A motorcomprising a stator 15 having a stator coil 14, a shaft 13, and a rotor16 fixed to the shaft 13 and having a permanent magnet 11 fixed to therotor, wherein the permanent magnet is made of a magnet comprisinggrains of a ferromagnetic material whose main component is iron and afluorine compound layer or an oxy-fluorine compound layer of fluoridecompound particles of alkali metals, alkaline earth metals and rareearth elements, present on the surface of the ferromagnetic materialgrains, wherein an amount of iron atoms in the fluorine compoundparticles is 1 to 50 atomic %.

The permanent magnet is supported by a soft magnet member 12 fixed tothe shaft 13.

Embodiment 10

In FIG. 8, a Ta under layer 22 having a thickness of 100 nm was formedby sputtering on a SiO₂ group substrate 23. An Nd₂Fe₁₄B film 21 having athickness of 1000 nm was formed on the

Ta under layer 22. A gelatin DyF₃.xH₂O solution containing Fe ions,which has been subjected to centrifugation, was coated with a spinner toform a coating of 1 to 1000 nm.

A resist 24 was coated on the fluorine compound layer 25, and the resistwas subjected to exposure and development thereby forming a resistpattern 24 as shown in (2).

Then, uncovered portions of the fluorine compound layer 25 were removedby an ion milling method as shown in (3). Thereafter, the resist maskwas removed with an organic solvent as shown in (4). The millimeter-waveheat treatment was applied to the film. As a millimeter-wave heater, a28 GHz millimeter-wave heating apparatus manufactured by Fuji DenpaIndustries was used to selectively heat the fluorine compound only.

The heating caused diffusion between the fluorine compound and the NdFeBfilm in contact with the fluorine compound thereby growing a reactionlayer 26, which resulted in change of magnetic properties of the NdFeBfilm. The reaction layer 26 may be formed only at the interface betweenthe fluorine compound layer 25 and NdFeB film.

Change of magnetic properties depends on kinds of fluorine compoundsused. When a fluorine compound such as DyF₃ or TbF₃ is used, change ofmagnetic properties such as improvement of coercive force of the NdFeBfilm near the contact point and suppression of thermal demagnetizationwere observed. Like that, it is possible to change only the portion ofthe NdFeB film in contact with the fluorine compound layer; an areawhere the magnetic properties changes is changed in accordance withsizes of the mask patterns. The pattern size may vary from sub-micronpatterns to larger patterns.

Magnetic properties of not only NdFeB, but also Fe group magnetic filmssuch as FePt, FeSiB, NiFe, etc or Co group magnetic films such as CoFe,CoPt, etc can be changed only at contact portions.

Since the millimeter-wave is used, it is possible to heat only thefluorine compound and in its vicinity, it is possible to heat selectedportions of the fluorine compound layer, which is formed all over thesurface of the fluorine compound layer. It is also possible to conductheat treatment without the under layer. This method can be applied tonot only magnetic recording media, but also to a partial heating ofmagnetic heads.

Further, NdFeB thick films having a thickness of 10 to 100 μm was formedafter forming a Ta under layer having a thickness of 10 nm or more by asputtering method.

In forming DyF₃, Dy (CH₃COO) ₃ was dissolved in water, and HF was addedthereto to obtain a gelatin like NdF3.xH2O. The gelatin was centrifugedand was coated on the thick film. Thereafter, the solvent was removed,and hydrated water was evaporated by heating. As a result, DyF₃ or DyF₂grew on the surface of the NdFeB thick film. The thickness of thefluorine compound was 1 to 100 nm. The fluorine compound layer can beformed by a sputtering method or evaporation method.

A millimeter-wave or microwave was irradiated to the fluorine compoundlayer to heat it so that Dy or F atoms were diffused from the surface ofNdFeB film. As a substrate, SiO2 glass, which is hard to be heated bymillimeter-wave or microwave, is suitable.

Diffusion of Dy and F atoms accompanies diffusion of Fe and Nd so thatthere was Fe in a concentration of 1 at %. At the same time,rectangularity and coercive force of NdFeB were improved. A thick filmmagnet having a residual magnetic flux density of 0.7 to 1.1T and acoercive force of 10 to 20 kOe was obtained.

Embodiment 11

A fluorine compound of rare earth element or alkaline earth metal wascoated on a soft magnetic plate in the following manner.

-   (1) A solution for forming a fluorine compound of Nd was prepared as    follows.

A water soluble salt of Nd was mixed with water and the salt wasdissolved under stirring. Diluted hydrofluoric acid was graduallydropped in the solution. The solution containing gelatinous precipitateof fluorine compound was further stirred and centrifuged. After thecentrifugation, methanol was added to the precipitate. The methanolsolution was stirred and centrifuged. Thereafter, methanol was added.After stirring of the methanol solution, and corrosive ions werediluted.

-   (2) The solution for coating NdF₃ was dropped into the methanol    solution, and the solution was stirred until the soft magnetic plate    was wet.-   (3) The soft magnetic plate coated with NdF₃ was subjected to    removal of methanol under a reduced pressure of 5 torr.-   (4) The soft magnetic plate was heated at 200° C. for 30 minutes and    400° C. for 30 minutes under a reduced pressure of 1×10⁻⁵ torr after    the solvent was removed.

Fe-Si-B (Si 10%, B 5%) amorphous sheet was selected from soft magneticplate was iron material such as amorphous sheet, electromagneticstainless plate and ferromagnetic material of Co or Ni. After thefluorine compound NdF₃ was coated on the Fe-Si-B amorphous sheet, thecoating was heated by millimeter-wave to heat only parts in contact withthe fluorine compound. When the fluorine compound is formed on selectedportion of the surface of the soft magnetic plate, only the portion ofthe fluorine compound layer of NdF₃ was heated by the millimeter-waveand Fe diffused into NdF₃ by 1 atomic %.

By heating selectively the coating, heated portion can be made low lossand non-heated portion can be made high mechanical strength. Whenelectromagnetic stainless steel plate partially coated with fluorinecompound is heated by millimeter-wave, only heated portion can bechanged from ferromagnetic plate to non-magnetic plate or fromnon-magnetic plate to ferromagnetic plate. Therefore, this technologycan be applied to an electric rotating machine.

Embodiment 12

Gelatinous or sol fluorine compound of rare earth elements was coated onan Nd₂Fe₁₄B sintered magnet. A thickness of the coating was 100 nm onaverage. The NdFeB sintered magnet has a main phase of Nd₂Fe₁₄B; thesurface of the magnet has deteriorated magnetic properties caused bymachining and polishing.

In order to improve the deteriorated magnetic properties, gelatinous orsol fluorine compound D_(y)F_(x) (x:1 to 3) of rare earth element wascoated on the surface of the sintered magnet and dried. Thereafter, themagnet was heat treated at a temperature of 500° C. or higher, but lowerthan a sintering temperature. The gelatinous or sol fluorine compound ofrare earth element grows into particles having a size of 1 to 100 nm,and diffusion or reaction takes place in grain boundaries or surfaceswhen heated.

Because the gelatinous or sol fluorine compound of rare earth element iscoated on the surface of the magnet, the fluorine compound D_(y)F_(x),D_(y) (O,F) , D_(y) (O, C, F) is formed along the crystal structure overalmost the whole surface of the magnet. After drying the coating andprior to heating at 500° C. to a temperature lower than the sinteringtemperature, a part of the coating where a concentration of rare earthelement is high on the surface of the magnet becomes fluorides.

Among the fluorine compounds of rare earth elements, Dy, Tb or Ho of Dyfluoride, Tb fluoride or Ho fluoride diffuses along the crystal grainsthere by to improve magnetic properties. If a heat treatment temperatureis 800° C. or higher, the mutual diffusion between the fluorine compoundand the sintered magnet proceeds further. A concentration of Fe of 10ppm or more is found.

As the heat treatment temperature becomes higher, a concentration of Fein the fluorine compound tends to become higher. If the Fe concentrationexceeds 50%, magnetic properties of the sintered magnet become worse.Accordingly, The concentration of Fe in the fluorine compound ispreferably 50% or less.

In bonding the stacked magnets mentioned above, another fluorinecompound was coated on the magnets with coatings of the fluorinecompound, which have been subjected to diffusion treatment; the stackedmagnets were irradiated with millimeter-wave thereby to bond them byheating only the bonding portions.

The fluorine compound as the bonding material is Nd compounds such as(NdF₂₋₃, Nd(OF)₁₋₃) , for example. By selecting irradiation conditions,it is possible to heat only the bonding parts selectively, whilesuppressing a temperature rise of the central part of the magnets. As aresult, deterioration of magnetic properties and dimension change of thesintered magnets can be prevented. At the same time, it is possible toshorten a heat treating time to half or less of the time required forthe conventional method. Thus, the method of heat-treating method of thepresent invention is highly productive.

Accordingly, the millimeter-wave can be used not only for bonding ofmagnets, but also for improving magnetic properties of the coatingmaterial by diffusion. Though it is possible to diffuse by heating,millimeter-wave can selectively heat the coating of fluorine compound;thus it can be used for bonding or adhesion of magnetic materials andmetallic materials. An example of conditions for millimeter-wave heatingis 28 GHz, 1 to 10 kW, and 1 to 30 minutes in an Ar atmosphere.

Since the millimeter heating causes only fluorine compounds oroxy-fluorine compounds that contain oxygen to generate heat, only thefluorine compound can be diffused along grain boundaries withoutchanging a structure of a sintered body. Therefore, it is possible toprevent elements constituting the fluorine compound from diffusion intograins of the magnet. As a result, high magnetic properties (highresidual magnetic flux density, good rectangularity, high coerciveforce, high Curie point, low thermal demagnetization, highanti-corrosion, high electric resistance, etc) are expected, compared tosimple heating. By selecting millimeter-wave conditions and fluorinecompounds, it is possible to diffuse constituting components of thefluorine compounds into deeper portions from the surface of the sinteredmagnet than the conventional heating method. Diffusion into the centerof a sintered magnet of 10×10×10 (cm) could be conducted.

Magnetic properties of the thus obtained sintered magnets exhibited aresidual magnetic flux density of 1.0 to 1.6T and a coercive force of 20to 50 kOe; it could be possible to make a concentration of rare earthelements lower than that of rare earth elements contained in aconventional comparative magnets (NdFeB magnetic powder containing heavyrare earth elements). Further, if a fluorine compound or an oxy-fluorinecompound containing at least one rare earth element remains on thesurface of the sintered magnet, a resistance of the surface of themagnet becomes high so that stacked and bonded magnets exhibit a reducededdy current loss and a reduced loss in a high magnetic field. Becauseof the reduced loss, which leads to low heat generation, an amount ofheavy rare earth element used can be reduced.

Since the fluorine compounds are not powder, they can be coated insidethe fine pores of 1 to 10 nm, and they can be applied to improvements ofminiature size magnets.

Instead of fluorine compounds, one or more of nitrogen compounds, carboncompounds or light element compounds such as boron compounds containingat least one rare earth element is coated on the surface of the NdFeBblocks. The coating is subjected to heating with millimeter-wave toachieve bonding of the blocks or improvement of magnetic properties.

Embodiment 13

2 atomic % of Fe was added to gelatinous or sol fluorine compound of afluorine compound containing MnF₂, MnF₃ to prepare a gelatinous or solFe-fluorine compound with which Fe ions or Fe clusters are admixed. Partof Fe atoms chemically reacts with fluorine or one or Mn constitutes thefluorine compounds.

When the gelatinous or sol fluorine compounds or precursors of thefluorine compounds are irradiated with millimeter wave or microwave toselectively heat the fluorine compound, there are a lot of atoms thatcontribute to chemical reaction of fluorine atoms and Fe atoms and oneor more of components constituting the fluorine compounds oroxy-fluorine compounds. As a result, fluorine compounds or oxy-fluorinecompounds of tertiary compounds comprising Fe atoms and two constitutingelements of the fluorine compounds are formed thereby to produce thefluorine compounds or oxy-fluorine compounds having a coercive force of10 kOe or more.

Fe or other transition metal ions may be added to the gelatinous or solsolution. According to the above-mentioned method, it is possible toobtain magnet materials, without employing conventional melting andcrushing steps.

If M represents any of elements selected from alkali metals, alkalineearth metals, Cr, Mn, V and rare earth elements, Fe-M-F group, Co-M-Fgroup and Ni-M-F group magnets are produced from gelatinous or solsolution, or fluorine compound solutions. The millimeter-waveirradiation makes it possible to form magnets on a substrate, which isnot molten by the millimeter-wave heating. The process can be applied toa magnet having a shape, which was not machined.

The fluorine compound magnet may contain oxygen, carbon, nitrogen,boron, etc, which give little influence on magnetic properties.

Embodiment 14

A gelatinous or sol fluorine compound was coated on the surface ofSm₂Fe₁₇N₃ group magnetic powder having a particle size of 7 μm. Thefluorine compound consists of GdF₃, GdF₂ and Gd (O,F). The fluorinecompound or its precursor was coated in a thickness of 1 to 100 nm onthe magnetic powder. The coated magnetic powder was charged in a moldand press-molded while orientating the magnetic powder in a magneticfield of 3 to 20 kOe to obtain a pre-molding. The thus obtained moldinghaving magnetic anisotropy was heated by irradiation with amillimeter-wave to selectively heat the fluorine compound consisting ofGdF₃, GdF₂, and Gd (O, F).

Deterioration of magnetic properties due to structure change duringheating was suppressed and the fluorine compound worked as a sinteringbinder thereby producing a magnetically isotropic magnet, wherein theSmFeN magnetic powder was bonded with the fluorine compound. When avolume of the fluorine compound consisting of GdF₃, GdF₂, and Gd (O,F)is 0.1 to 3%, the SmFeN anisotropic magnet with a residual magnetic fluxdensity of 1.0T or more was obtained.

It is possible to improve magnetic properties by heat-treating thepre-molding after the pre-molding is impregnated with the fluorinecompound. (Sm, Gd)₂Fe₁₇(N,F)₃ or (Sm, Gd)₂Fe₁₇(N,F,O)₃ are locallyformed. By the reaction with the fluorine compounds, it was confirmedthat there was any of an increase in coercive force, rectangularity andresidual magnetic flux density.

In case of nitrogen group magnetic powder such as SmFeN, when the SmFeNpowder is heated by irradiation with the millimeter-wave to produceSmFeN magnetic powder, it is possible to obtain a coercive force of 20kOe, because an increase in the coercive force is remarkable in themillimeter-wave heating, compared to a conventional ammonianitrogenation. The bonding the powder with the fluorine compound bymillimeter-wave can be applied to other iron group materials such asFe-Si, Fe-C, Fe-Ni, Fe-Co or Fe-Si-B, and Co group materials. Thistechnique can be applied to soft magnetic powders, soft magnetic foils,soft magnetic moldings, hard magnetic powders, hard magnetic foils, andhard magnetic moldings. Other metallic materials can be bonded.

Further, the fluorine compounds are NdF₃, LiF, MgF₂, CaF₂, ScF₂, VF₂,VF₃, CrF₂, CrF₃, MnF₂, MnF₃, CoF₂, CoF₃, NiF₂, ZnF₂, AlF₃, GaF₃, SrF₂,YF₃, ZrF₃, NbF₅, AgF, InF₃, SnF₂, SnF₄, BaF₂, LaF₂, LaF₂, CeF₃, PrF₂,PrF₃, NdF₂, SmF₂, SmF₃, EuF₂, EuF₃, GdF₃, TbF₃, TbF₄, DyF₂, DyF₃, HoF₂,HoF₃, ErF₂, ErF₃, TmF₂, TmF₃, YbF₂, YbF₃, LuF₂, LuF₃, PbF₂, and BiF₃, oroxygen containing fluorine compounds or carbon containing compounds thatare formed by surface treated compounds with a solution containingoxygen or carbon.

Embodiment 15

Fine particles of FeF₁₋₃ containing Fe and having a particle size of 5μm was added to a gelatinous or sol fluorine compound GdF₃ to produce agelatinous or sol fluorine compound. Fe atoms on the surface of the fineparticles chemically bonded with any of alkali metals, alkaline earthmetals, or rare earth elements that constitute the fluorine compound.Irradiation with the millimeter-wave or microwave to the gelatinous orsol fluorine compound GdF₃ containing the fine particles increases atomsthat contribute to chemical bonding between fluorine atoms and Fe atomsor constituting elements Gd for the fluorine compound so that ternary ormore fluorine compound containing Fe-fluorine and the constitutingelement is formed. The irradiation with the millimeter-wave or microwaveproduces a fluorine compound having a coercive force of 10 kOe or more.

Instead of Fe fine particles, other transition metal fine particles canbe added. Fe or other transition metal ions may be added to thegelatinous or sol solution. According to the above-mentioned method, itis possible to obtain magnet materials without employing conventionalmelting and crushing steps.

If M represents any of elements selected from alkali metals, alkalineearth metals, Cr, Mn, V and rare earth elements, Fe-M-F group, Co-M-Fgroup and Ni-M-F group magnets are produced from gelatinous or solsolution, or fluorine compound solutions. The millimeter-waveirradiation makes it possible to form magnets on a substrate, which isnot molten by the millimeter-wave heating. The process can be applied toa magnet having a shape, which is not machined.

The fluorine compound magnet may contain oxygen, carbon, nitrogen,boron, etc, which give little influence on magnetic properties.

The gelatinous or sol fluorine compound was inserted into patternsprepared by a resist mask, etc, followed by drying and heat-treatment ata temperature lower than a heat-resistant temperature of the resist.After removing the resist, the particles were heated to increase thecoercive force.

The gelatinous or sol fluorine compound could be injected into or coatedin spaces of resist patterns having a width of 10 nm or more and athickness of magnet portion of 1 nm or more. Thus, a three dimensionalmagnet could be prepared without machining, or physical processes suchas evaporation, sputtering, etc. The Fe-M-F magnet can absorb only lighthaving a specific wavelength. Accordingly, the fluorine compound can beused as optical components, or parts for optical recording devices, oras a surface treating agent.

As the fluorine compounds there are R2Fe17F2-3 (R: Li, Mg, Ca, Sc, V,Mn, Co, Ni, Zn, Al, Ga, Sr, Y, Zr, Nb, Ag, In, Sn, Ba, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Ho, Er, Tm, Yb, Lu, Pb) or an oxygen containing fluorinecompound, carbon containing compounds that are formed by a surfacetreating the above fluorine compounds with a solution containing oxygenor carbon. Using the fluorine compounds, magnets having a coercive forceof 10 to 30 Oe are obtained.

Embodiment 16

Particles of NdFeB having a particle size of 10 nm and containing atleast one rare earth elements were added to a gelatinous or sol fluorinecompound of GdF₃. The particles contain Nd₂Fe₁₄B as a main component.The mixture was coated on the surface of the particles. As a parameterfor coating conditions, a mixing ratio of the fluorine compound and theparticles was changed to change a covering rate of the particles. Whenthe covering rate is 5%, an increase in coercive force by the fluorinecompound was recognized, and when the covering rate is 30%, an increasein rectangularity of demagnetization curve or Hk in addition to theincrease in the coercive force was recognized. When the covering rate is80%, an increase in resistance of a molding was recognized. In theabove, the covering rate is a rate of an area of a coating material(fluorine compound) covering the particles per a surface area of theparticles.

Particles whose covering rate is 1 to 10% were pre-molded in a magneticfield, and the molding was heat-molded at 800° C. or higher to produce asintered magnet. The gelatinous or sol fluorine compound contains atleast one rare earth element. Since the fluorine compound is agelatinous or sol solution, it was coated along the grain boundaries.Even if there are uneven faces on the particles, the solution can becoated along the shapes of the surface.

The rare earth elements of the fluorine compound diffuse along the grainboundaries of the particles during the heat-treatment after pre-moldingin the magnetic field. As a result, a coercive force was increasedcompared to the case where no coating was formed on the particles.

When the gelatinous or sol fluorine compound is coated on Fe groupparticles, exposed Fe particles wherein no coating is formed becomesfluoride. Accordingly, since 90% of the surface of the Fe particles isexposed, the exposed surface is changed to fluoride so that magneticproperties at the grain boundaries change and resistance of the surfaceincreases.

Since the rare earth elements easily react with fluorine to form afluoride, the surface of the particles change into the fluoride when theparticles are coated with the solution if a concentration of rare earthelements is high. If the particles with a high resistance are sintered,rare earth elements in the inside of the particles react with fluorinein the surface thereof to segregate rare earth elements in the vicinityof the grain boundaries, thereby increasing the coercive force. Fluorineworks as a trapping agent, and it suppresses diffusion of the rare earthelement (Nd) in the particles to thereby segregate the rare earthelements in the grain boundaries to increase the coercive force andlower a concentration of the rare earth elements (Nd) in the particles,which leads to a high residual magnetic flux density.

Embodiment 17

Particles of rare earth elements such as Nd₂Fe₁₄B as a main phase havinga particle size of 1 to 10000 nm and containing at least one rare earthelements were added to a gelatinous or sol fluorine compound solution.The particles or fine magnets contain Nd₂Fe₁₄B as a main component. Thegelatinous or sol fluorine compound solution contacts with the surfacesof the particles. The fluorine compound adhered to the surfaces of theparticles was removed with a solvent. An amount of the fluorine compoundremaining on the surface of the particles should be as small aspossible, preferably 10% or less on an average coverage rate.Accordingly, 90% or more of the surface of the particles is exposed.This was confirmed by observation with a scanning electron microscope at10000 magnitudes. In a part of the surface, part of the rare earthelement was changed to fluoride, which is rich in fluorine. Rare earthelements tend to react easily with fluorine to form a fluoride, but ifthe rare earth elements (Nd) do not exist, the reaction for formingfluoride is hard to occur.

In case where a part of the rare earth elements (Nd) forms a fluoride, alayer of fluoride of rare earth elements is formed on the surface of theparticles. Since the rare earth elements easily react with oxygen,oxy-fluorine compound may be formed besides the fluoride.

The particles with the fluoride layer were press-molded in a magneticfield, followed by sintering to form anisotropic sintered magnet.

The resulting molding having a density of 50 to 90% was impregnated withthe above-mentioned fluorine solution. The surface of the particles canbe covered with a precursor of the fluorine compound. With theimpregnation treatment, the fluorine compound having a thickness of 1 to100 nm was formed on the particles to cover the surface and cracks. Thisstructure contributes to any of increases in coercive force,rectangularity and resistance and a decrease in residual magnetic fluxdensity, reduction of an amount of rare earth elements used, an increasein strength, and imparting anisotropy to the magnetic powder.

Sintering accompanies diffusion of fluorine atoms and rare earthelements. The larger the additive amount of heavy rare earth elements,the larger the coercive force becomes by virtue of forming the fluoride,compared to a case where the fluoride is not formed. A concentration ofthe heavy rare earth elements can be reduced by forming the fluoridethereby to obtain the same coercive force. The heavy rare earth elementstend to segregate in the vicinity of fluoride phase so that a structurewhere the heavy rare earth elements segregated to increase the coerciveforce. A width of the segregation is about 1 to 100 nm from the grainboundaries.

Embodiment 18

A fluorine compound solution of GdF3 a main phase, Gd(O,F)and Gd(O,F,C)was coated on oxide powder BaFe_(l2)Co_(0.5)Ti_(0.1)O₁₉ and having aparticle size of 10 nm; then the powder was heated at 1200° C. andirradiated with a millimeter-wave. An oxy-fluorine compound(Gd,Fe)_(x)O_(y)F_(z) (x,y,z: integers) was partially formed on thesurface of the particles at the time of heating. As the fluorinecompound solution containing at least one rare earth element, formationof oxy-fluorine compound or fluorine compound improved magneticproperties of barium ferrite oxide or strontium ferrite oxide. Anincrease in the coercive force, rectangularity of demagnetization curveand residual magnetic flux density were confirmed. Particularly, if afluorine compound solution containing lat% of Fe was used, an effect ofincrease in the residual magnetic flux density was remarkable. The oxidepowder treated with the fluorine compound can be prepared by a sol-gelprocess.

Embodiment 19

10 atomic % Fe was added to a gelatinous or sol state fluorine compoundsolution of GdF3 or a solution containing oxygen or carbon to prepare agelatinous or sol Co- or Ni-fluorine compound solution wherein Fe ionscluster are mixed. Part of Fe atoms reacts with Gd or fluorine atoms oralkali metals, alkaline earth metals or rare earth elements thatconstitute the fluorine compound.

When the gelatinous or sol fluorine compound or its precursor isirradiated with a millimeter-wave or microwave to dry the compound sothat the number of atoms that contribute to chemical bond among fluorineatoms, Fe atoms and at least one rare earth elements increases to formternary or more fluorine compounds. By irradiation with themillimeter-wave or microwave, it is possible to prepare a fluorinecompound having a coercive force of 10 kOe or more. A part of Fe ionsmay be substituted by rare earth element ions. It is possible to obtainmagnetic powder without dissolution and crushing steps according to theabove method. Accordingly, this method can be applied to a magneticcircuit.

If M represents any of elements selected from alkali metals, alkalineearth metals and rare earth elements, Co-M-F group, Co-M-F group andNi-M-F group magnets are produced from gelatinous or sol solution, orfluorine compound solutions. The millimeter-wave irradiation makes itpossible to form magnets on a substrate, which is not molten by themillimeter-wave heating. The process can be applied to a magnet having ashape, which is not machined.

The fluorine compound magnet may contain oxygen, carbon, nitrogen,boron, etc, which give little influence on magnetic properties.

Embodiment 20

Fine particles of Fe having a particle size of 1 to 100 nm was added toa gelatinous or sol fluorine compound of GdF₃ or a compound of GdF₃containing oxygen or carbon to produce a gelatinous or sol Fe-fluorinecompound. Fe atoms on the surface of the fine particles chemicallybonded with Gd constituting the fluorine compound. Irradiation with themillimeter-wave or microwave to the gelatinous or sol fluorine compoundcontaining the fine particles increases atoms of Gd that contribute tochemical bonding between fluorine atoms and Fe atoms or constitutingelements for the fluorine compound. Fe atoms and Gd bond by means offluorine atoms or bonds between fluorine atoms and oxygen atoms so thatmagnetization of Fe becomes ferromagnetic.

Irradiation with a millimeter-wave or microwave produces a structurethat is useful for the ferromagnetic bonds thereby producing fluorinecompound containing Fe having a coercive force of 10 kOe. In place of Fegroup fine powder, fine powder of other transition metals may be added.That is, in case of transition metals such as Cr, Mn, V, etc other thanCo and Ni, the above method can be employed. Therefore, permanent magnetmaterials can be produced without dissolution and crushing; the methodcan be applied to a magnetic circuit, accordingly.

Embodiment 21

Fine particles of Fe having a particle size of 1 to 100 nm was added toa gelatinous or sol fluorine compound of GdF₃ or the compound containingoxygen or carbon to produce a gelatinous or sol Fe-fluorine compound. Featoms on the surface of the fine particles chemically bonded with Gdthat constitute the fluorine compound. Irradiation with themillimeter-wave or microwave to the gelatinous or sol fluorine compoundcontaining the fine particles increases atoms that contribute tochemical bonding between fluorine atoms and Fe atoms or constitutingelements for the fluorine compound. Fe atoms and rare earth elementsbond by means of fluorine atoms or bonds between fluorine atoms andoxygen atoms so that magnetization of Fe becomes ferromagnetic andexhibits magnetic anisotropy.

A fluorine rich phase (F: 10 to 50%), a Fe rich phase (Fe: 50 to 85%)and a rare earth element rich phase (rare earth element: 20 to 75%) areformed in the fine powder. The Fe rich phase bears magnetization, thefluorine rich phase or rare earth element rich phase bears high coerciveforce. Magnetization of part of Fe atoms takes anti-ferromagnetic bonds.

Irradiation with a millimeter-wave or microwave produces a structurethat is useful for the ferromagnetic bonds thereby producing fluorinecompound containing Fe having a coercive force of 10 kOe. In place of Fegroup fine powder, fine powder of other transition metals may be added.Therefore, permanent magnet materials can be produced withoutdissolution and crushing; the method can be applied to a magneticcircuit, accordingly.

Embodiment 22

A gelatinous or sol fluorine-rare earth element compound was coated onthe NdFeB sintered magnet whose main component was Nd₂Fe₁₄B. An averagethickness of the fluorine-rare earth element compound coating of DyF₂was 5 nm. A crystal grain size of the NdFeB sintered magnet had 5 μm onaverage and its main component is Nd₂Fe₁₄B. Deterioration of magneticproperties in demagnetization curve due to surface machining orpolishing was observed in the surface of the sintered magnet. In orderto improve the deteriorated magnetic properties, increase a coerciveforce by segregation of rare earth elements in the vicinity of grainboundaries, rectangularity of demagnetization curve, resistance in thesurface of the magnet or in the vicinity of grain boundaries, a Curiepoint by the fluorine compound and mechanical strength, improveanti-corrosion, reduce an amount of rare earth element used and reducemagnetization field, etc, the gelatinous or sol rare earthelement-fluorine compound solution of DyF₂ was coated on the sinteredmagnet and dried. The magnet was heat-treated at 500° C. or higher butlower than the sintering temperature.

The gelatinous or sol like rare earth element-fluorine compoundparticles grow to 1 to 100 nm grains immediately after coating anddrying. A further heating brings about reaction or diffusion betweengrains of the sintered magnet and the surface. The gelatinous or solrare earth element-fluorine compound powder grew to particles of 1 to100 nm, immediately after coating and drying. When the particles wereheated further, reaction and diffusion took place in the grainboundaries and surfaces.

Since the fluorine compound particles after coating and drying were notsubjected to a crushing process, projections or keen corners were notfound in the surface. When the particles were observed with atransmission electron microscope, the particles were egg like orspherical, but cracks were not found. When heated, they agglomerated andgrew, and at the same time, the particles diffused along the grainboundaries or mutually diffused with the constituting components of thesintered magnet. Further, because the gelatinous or sol rare earthelement-fluorine compound was coated on the magnet with the sinteredmagnet, almost entire of the surface of the magnet was covered with thecoating. Therefore, before the coating is heated at 500° C. or higherbut lower than the sintering temperature, part of the particles where aconcentration of rare earth element of the sintered magnet was highturned into fluoride.

The fluoride phase or fluoride phase containing oxygen grew in harmonywith the mother phase. The fluorine compound phase or oxy-fluorinecompound phase grew outside the fluoride mother phase or oxy-fluoridemother phase, wherein heavy rare earth elements segregated in thesephases to increase coercive force.

A belt like portion wherein the heavy rare earth elements areconcentrated should preferably have a width of 1 to 100 nm. This widthsatisfied the high residual magnetic flux density and high coerciveforce. If Dy was concentrated along the grain boundaries by the abovemethod, the resulting sintered magnet had a residual magnetic fluxdensity of 1.0 to 1.6T and a coercive force of 20 to 50 kOe.

The concentration of the heavy rare earth elements in the sinteredmagnet of this embodiment was lower than that of a conventional magnetthat used NdFeB powder containing added heavy rare earth elements, whichis equivalent to the magnet of this embodiment.

A concentration of Fe in the fluorine compound of the sintered magnetchanged in accordance with heat-treatment temperature; when heated at1000° C. or higher, Fe of 10 ppm to 5% diffused into the fluorinecompound. Though the concentration of fluorine in the vicinity of thegrain boundaries became 50%, the concentration hardly affects onmagnetic properties of the sintered magnet as long as the concentrationis 1 to 5%.

Embodiment 23

Fine particles of Fe having a particle size of 100 nm on average wasadded to a gelatinous or sol fluorine compound of SmF₃ to produce agelatinous or sol Fe fine particle containing fluorine compound.

Part of Fe atoms on the surface of the fine particles chemically bondedwith any of alkali metals, alkaline earth metals, or rare earth elementsthat constitute the fluorine compound. Irradiation with themillimeter-wave or microwave to the gelatinous or sol fluorine compoundcontaining the fine particles or its precursor increases atoms thatcontribute to chemical bonding between fluorine atoms SmF₂ and Fe atomsor constituting elements for the fluorine compound. Fe atoms and rareearth elements bond by means of fluorine atoms or bonds between fluorineatoms and oxygen atoms so that magnetization of Fe becomes ferromagneticand exhibits magnetic anisotropy.

A fluorine rich phase (F: 10 to 50%), a nitrogen rich phase (N: 3 to20%), a Fe rich phase (Fe: 50 to 85%) and a rare earth element richphase (rare earth element: 10 to 75%) are formed in the fine powder. TheFe rich phase bears magnetization, the fluorine rich phase or rare earthelement rich phase bears high coercive force. It is possible to producea magnet having a coercive force of 10 kOe or more from the fourelements Fe-M-F-N (M: rare earth element, alkali metal or alkaline earthmetal).

Embodiment 24

Fine particles of Fe-5% B alloy having a particle size of 100 nm wasadded to a gelatinous or sol fluorine compound of NdF₂ or a compound ofNdF₂ containing oxygen or carbon to produce a gelatinous or solFe-fluorine compound containing Fe-B fine powder.

If the particle size of the fine powder exceeds 100 nm, magneticproperties inherent to Fe, which is a soft magnetic material, remainafter the processing, and if the particle size is 1 nm or less, aconcentration of oxygen with respect to Fe becomes high so thatimprovement of magnetic properties becomes difficult. Accordingly, aparticle size of 1 to 100 nm is preferable.

Part of Fe atoms on the surface of the Fe-B fine particles chemicallybonded with any of alkali metals, alkaline earth metals, or rare earthelements that constitute the fluorine compound. Irradiation with themillimeter-wave or microwave to the gelatinous or sol fluorine compoundcontaining the Fe-B fine particles or its precursor increases atoms thatcontribute to chemical bonding between fluorine atoms and Fe atoms orconstituting elements for the fluorine compound. Fe atoms and rare earthelements bond by means of fluorine atoms. Bonding among fluorine atoms,boron atoms, Fe atoms, rare earth elements, or bonding of rare earthelements to fluorine, oxygen atoms, boron atoms and Fe atoms makesmagnetization of fluorine rich phase ferromagnetic to exhibit magneticanisotropy.

A fluorine rich phase (F: 10 to 50%), a boron rich phase (B: 3 to 20%),a Fe rich phase (Fe: 50 to 85%) and a rare earth element rich phase(rare earth element: 10 to 75%) are formed in the fine powder. The Ferich phase bears magnetization, the fluorine rich phase, boron richphase or rare earth element rich phase bears high coercive force. It ispossible to produce a magnet having a coercive force of 10 kOe or morefrom the four elements Fe-M-B-F (M: rare earth element, alkali metal oralkaline earth metal). Because M is a heavy rare earth element, a Curiepoint becomes 400 to 600° C.

Embodiment 25

A gelatinous or sol fluorine-rare earth element compound or itsprecursor that is capable of growing to rare earth element-fluorinecompound was coated on the NdFeB sintered magnet whose main componentwas Nd₂Fe₁₄B. An average thickness of the fluorine-rare earth elementcompound coating was 1 to 10000 nm. A crystal grain size of the NdFeBsintered magnet had 1 to 20 μm on average and its main component isNd₂Fe₁₄B. Deterioration of magnetic properties in demagnetization curvedue to surface machining or polishing was observed in the surface of thesintered magnet. In order to improve the deteriorated magneticproperties, increase a coercive force by segregation of rare earthelements in the vicinity of grain boundaries, rectangularity ofdemagnetization curve, resistance in the surface of the magnet or in thevicinity of grain boundaries, a Curie point by the fluorine compound andmechanical strength, improve anti-corrosion, reduce an amount of rareearth element used and reduce magnetization field, etc, the gelatinousor sol rare earth element-fluorine compound solution was coated on thesintered magnet and dried. The magnet was heat-treated at 500° C. orhigher but lower than the sintering temperature.

The gelatinous or sol like rare earth element-fluorine compoundparticles grow to 1 to 100 nm grains immediately after coating anddrying. A further heating brings about reaction or diffusion betweengrains of the sintered magnet and the surface.

Particles of the fluorine compound powder after coating and drying haveno projections or keen angle portions if the temperature is within arange where the particles do not agglomerate, because the particles arenot subjected to a crushing process. When the particles are observedwith a transmission electron microscope, they are round, egg like formor spherical, and cracks or non-continuous unevenness in the inside ofthe particles or the surface thereof. When the particles are heattreated, these particles agglomerate on the surface of the sinteredmagnet, and at the same time, they diffuse along the grain boundaries ormutually diffuse with constituting elements of the sintered magnet.

Further, because the gelatinous or sol rare earth element-fluorinecompound was coated on the magnet with the sintered magnet, almostentire of the surface of the magnet was covered with the coating. Aftercoating and drying the coating, part of the surface of the particles ofthe sintered magnet where a concentration of rare earth elements is highbecame fluoride.

The fluoride phase or fluoride phase containing oxygen grew in harmonywith the mother phase. The fluorine compound phase or oxy-fluorinecompound phase grew outside the fluoride mother phase or oxy-fluoridemother phase, wherein heavy rare earth elements segregated in thesephases to increase coercive force.

A belt like portion wherein the heavy rare earth elements areconcentrated should preferably have a width of 0.1 to 100 nm. This widthsatisfied the high residual magnetic flux density and high coerciveforce.

Using a precursor of DyF₂₋₃, Dy was concentrated along the grainboundaries in accordance with the above method. The resulting sinteredmagnet had a residual magnetic flux density of 1.0 to 1.6T and acoercive force of 20 to 50 kOe.

The concentration of the heavy rare earth elements in the sinteredmagnet of this embodiment was lower than that of a conventional magnetthat used NdFeB powder containing added heavy rare earth elements, whichis equivalent to the magnet of this embodiment.

A concentration of Fe in the fluorine compound of the sintered magnetchanged in accordance with heat-treatment temperature; when heated at1000° C. or higher, Fe of 10 ppm to 5% diffused into the fluorinecompound. Though the concentration of fluorine in the vicinity of thegrain boundaries became 50%, the concentration hardly affects onmagnetic properties of the sintered magnet as long as the concentrationis 5% or less.

Embodiment 26

Sm₂(Fe_(0.9)Co_(0.1))₁₇ alloy was melted by high frequency melting, etcand an ingot was crushed in inert gas. Crushed powder had a size of 1 to10 μm. The powder was coated with a precursor of fluorine compound (SmF₃precursor) and the coating was dried. The coated powder was oriented bya press machine in a magnetic field to produce a compacted molding. Manycracks were introduced into powder of the compacted molding. Theprecursor was impregnated in the compacted molding to cover part of thecracks with the precursor. The resulting body was sintered and quenched.

The sintered body comprised at least two phases of Sm(Fe_(0.9)Co_(0.1))₅and Sm₂(Fe_(0.9)Co_(0.1))₁₇. The fluorine compound began to bedecomposed at the time of sintering, and fluorine atoms distributed morein the Sm(Fe_(0.9)Co_(0.1))₅ phase, though they are present in bothphases. The coercive force increased, compared to a case where noprecursor was added. It was confirmed that coating of the fluorinecompound precursor improved at least one of high resistance,rectangularity, and demagnetization withstanding.

Embodiment 27

Powder having a main component close to Nd₂Fe₁₄B and a particle size of1 to 20 μm was pre-molded in a magnetic field in an inert gas atmosphereor in vacuum at 500 to 1000° C., and a fluorine compound precursorsolution of DyF₃ was impregnated in or coated on the molding. Thesolution entered into the molding along the grain boundaries, part ofthe grain boundaries were covered with the precursor.

Then, the impregnated or coated molding was sintered at a temperaturehigher than the above temperature, and was subjected to heat treatmentat a lower temperature to increase a coercive force. As a result, asintered body containing fluorine, rare earth elements Dy, alkali metalsor alkaline metals for constituting the precursor was obtained. Afeature of this process is to form a rare earth element rich phase onpart or entire of the surface of the magnetic powder, followed byforming gaps of 1 nm or larger between the magnetic powder except thecontact points, without complete sintering, and to fill the gaps withthe precursor of the fluorine compound of Dy by impregnation or coating.As a result, part of the magnetic powder in the molding is covered withthe precursor of the fluorine compound.

According to this process, it is possible to coat the magnetic powderwith the precursor even in the center portion of the sintered bodyhaving a size of 100 mm. By using heavy rare earth element such as Dy,Tb, etc, the heavy rare earth element was segregated in the vicinity ofgrain boundaries of the sintered body.

It was possible to improve coercive force, rectangularity and residualmagnetic flux density, to reduce a temperature coefficient of coerciveforce and of residual magnetic flux density, or to reduce deteriorationof magnetic properties caused by machining.

Segregation of the heavy rare earth element takes place within a rangeof 1 to 100 nm from the grain boundaries, and the width changesdepending on heat treatment temperatures. The width tends to spread at aspecific point such as grain boundary triple point.

Embodiment 28

A solution of gel, sol or precursor of an Fe fluorine compound of FeF₂was mixed with a precursor of a fluorine compound GdF₃. The mixture wasdried and heat-treated to obtain compounds represented by Gd₂Fe₁₇F₁₋₃.

Because the precursor was used, grains that grew during the drying andheat-treatment were as small as 1 to 30 nm. The fluorine compound grewin the nano-particles.

The fluorine compound material having a high coercive force can beproduced by forming an M rich phase of 10 atomic % of Fe and 1 atomic %of F in the grain boundaries. Particularly, concentrations of Fe, andfluorine suitable for forming fluorine rich phase, Fe rich phase and Gdrich phase are 50 atomic % or more, 5 to 30% and 1 to 20%, respectively.

Forming the fluorine rich phase or M rich phase in the grain boundariesproduces magnetic powder exhibiting ferromagnetism and having a coerciveforce of 10 kOe or more. When the fluorine compound grows in a magneticfield to impart anisotropy thereto, the Fe rich phase grows along themagnetic field. Even if hydrogen, oxygen, carbon, nitrogen and boronenters the phase during the growth process, there is no problem as longas the structure of the phase is maintained.

If Fe-M-F (M: at least one of transition metals such as Cr, Mn, etc),which has M atoms of 5 atomic % and F atoms of 5 atomic %, is grown froma solution containing gel, sol or a precursor of fluorine compound, ahigh coercive force is expected. Because the ternary magnet is producedfrom the solution, machining and polishing steps are not necessary.Therefore, magnets of complicated figures can be easily manufactured. Itis possible to change directions of anisotropy in a magnet. The magnetis applicable to various rotating machines, magnetic sensors, magnetparts for hard discs, magnetic recording media, etc.

If a concentration of M is less than 5 atomic %, the ternary Fe-M-Falloy becomes high saturated magnetic flux density material, which issuitable for core materials for various magnetic circuits.

Embodiment 29

A rotor for an electric rotating machine was manufactured by bonding anNdFeB sintered magnet whose main component is Nd₂Fe₁₄B to laminatedelectro-magnetic steel plates, laminated amorphous plates or compactediron. The laminated electro-magnetic steel plates or compacted iron wereshaped by a metal mold in advance. When a sintered magnet is insertedinto positions into which magnets are inserted, a small gap of 0.01 to0.5 mm was formed between the sintered magnet and the laminatedelectro-magnetic steel plates.

Sintered magnets having a rectangular form, ring-form or rod form wereinserted into the portions, and the gaps were filled with a gelatinousor sol fluorine compound solution and heated at 100° C. or higher,thereby bonding the members. The members were further heated at 500° C.to diffuse rare earth element or fluorine into the surfaces of themagnets and of the electro-magnetic steel plates. As a result, magneticproperties (coercive force, rectangularity, anti-demagnetization, Curiepoint, etc) of the sintered magnets were improved.

It is possible to improve magnetic properties of machined magnets, whichhave transformed layers with curve faces by machining. A diffusion layercontaining fluorine or rare earth elements in the surface and grainboundaries of the magnetic materials may contain light elements such asoxygen or carbon. In order to improve magnetic properties of thesintered magnets, the fluorine compound should contain rare earthelements. In order to improve bonding, stress relieving of the softmagnetic material or loss reduction, fluorine compounds that containrare earth elements, alkali metals or alkaline earth metals should beused.

In some of the embodiments of the present invention, a layer having ahigher resistance than the magnets is formed in part of grainboundaries. The high resistance layer contains Fe. It is possible tochange re-coil permeability or other magnetic properties by controllingthe Fe concentration. The magnets of the embodiments that meet magneticcircuits can be applied to magnet motors. The magnet motors are used inapplications including driving motors for hybrid-cars, starters, powerstealing systems.

1. A magnet composed of united particles of a ferromagnetic materialwhose main component is iron, each of the particles comprising theferromagnetic material and a layer of a fluorine compound of at leastone member selected from the group consisting of alkali metals, alkalineearth metals and transition metals, coated on surfaces of the particles,wherein the layer of the fluorine compound contains iron in a range offrom 1 to 50 atomic %, and the fluorine compound has a face-centeredcubic crystal structure.
 2. The magnet according to claim 1, wherein theface-centered cubic crystal structure has a lattice constant of 0.54 to0.60 nm.
 3. The magnet according to claim 1, wherein the ferromagneticmaterial comprises a fluorine-rich phase, an iron-rich phase and a rareearth-rich phase.
 4. The magnet according to claim 1, wherein thefluorine compound is one of a fluoride, an oxy-fluoride and a mixturethereof.
 5. The magnet according to claim 1, wherein the ferromagneticmaterial is represented by R-Fe-B, wherein R is a rare earth metal, Feis iron, and B is boron.
 6. The magnet according to claim 1, wherein thefluorine compound is at least one member selected from the groupconsisting of NdF₃LiF, MgF₂, CaF₂, ScF₂, VF₂, VF₃, CrF₂, CrF₃, MnF₂,MnF₃, CoF₂, CoF₃, NiF₂, ZnF₂, AIF₃, GaF₃, SrF₃, YF₃, ZrF₃, NbF₅, AgF,InF₃, SnF₂, SnF₄, BaF₂, LaF₂, LaF₃, CeF₃, PrF₃, NdF₂, SmF₂, SmF₃, EuF₂,EuF₃, GdF₃, TbF₃, TbF₄, DyF₂, DyF₃, HoF₂, HoF₃, ErF₂, ErF₃, TmF₂, TmF₃,YbF₂, YbF₃, LuF₂, LuF₃, PbF₂, and BiF₃.
 7. The magnet according to claim1, wherein the fluorine compound has a particle size of 1 to 500 nm. 8.The magnet according to claim 1, wherein the fluorine compound has ahigher electric resistance than that of the particles of theferromagnetic material.
 9. The magnet according to claim 1, wherein themagnet has a recoil magnetic permeability of 1.04 to 1.30.
 10. Themagnet according to claim 1, wherein the specific resistance is 0.2mΩcmor more.
 11. The magnet according to claim 1, wherein the oxy-fluorinecompound is represented by Rw(OxFy)z wherein w,x,y and z are integersand R is at least one member selected from the group consisting of Li,Mg, Ca, Sc, Mn, Co, Ni, Zn, AI, Ga, Sr, Y, Zr, Nb, Ag, In, Sn, Ba, La,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Pb and Bi.
 12. Themagnet according to claim 1, wherein a particle size of the particles is1 to 300 μm.
 13. The magnet according to claim 1, wherein the layer offluorine compound is formed between NdFeB system particles and Feparticles.
 14. A magnet composed of united particles of a ferromagneticmaterial whose main component is iron, each of the particles comprisingthe ferromagnetic material and a layer of a fluorine compound of atleast one member selected from the group consisting of alkali metals,alkaline earth metals and transition metals, coated on surfaces of theparticles, wherein the fluorine compound has a face-centered cubiccrystal structure wherein the layer of the fluorine compound comprisesiron in an amount of 50 atomic % or more, at least one member selectedfrom the group consisting of alkali metals, alkaline earth metals andtransition metals in an amount of 5 to 30% atomic % and fluorine in anamount of 1 to 20% atomic %.
 15. The magnet according to claim 14,wherein the face-centered cubic crystal structure has a lattice constantof 0.54 to 0.60 nm.
 16. The magnet according to claim 14, wherein theferromagnetic material comprises fluorine-rich phase, an iron-rich phaseand a rare earth-rich phase.
 17. The magnet according to claim 14,wherein the fluorine compound is one of a fluoride, an oxy-fluoride anda mixture thereof.
 18. The magnet according to claim 14, wherein theferromagnetic material is represented by R-Fe-B, wherein R is a rareearth metal, Fe is iron, and B is boron.
 19. The magnet according toclaim 14, wherein the fluorine compound has a higher electric resistancethan that of the particles of the ferromagnetic material.
 20. The magnetaccording to claim 14, wherein the magnet has a recoil magneticpermeability of 1.04 to 1.30.
 21. The magnet according to claim 14,wherein the specific resistance is 0.2mΩcm or more.
 22. The magnetaccording to claim 14, wherein a particle size of the particles is 1 to300 μm.
 23. A magnet composed of united particles of a ferromagneticmaterial whose main component is iron, each of the particles comprisingthe ferromagnetic material and a layer of a fluorine compound of atleast one member selected from the group consisting of alkali metals,alkaline earth metals and transition metals, wherein the particlescomprise the iron in an amount of 50 atomic % or more, said at least onemember in an amount of 5 to 30 atomic % and the fluorine in an amount of1 to 20 atomic %.
 24. The magnet according to claim 23, wherein theparticles contain atoms of hydrogen, oxygen, carbon, nitrogen and boron.25. The magnet according to claim 23, wherein a particle size of theparticles is 1 to 300 μm.